The master of humorous fantasy delivers one of his strongest, most conventional books yet. Discworld's equivalent of Santa Claus, the Hogfather (who flies in a sleigh drawn by four gigantic pigs), has been spirited away by a repulsive assassin, Mr. Teatime, acting on behalf of the Auditors who rule the universe and who would prefer that it exhibited no life. Since faith is essential to life, destroying belief in the Hogfather would be a major blow to humanity. It falls to a marvelously depicted Death and his granddaughter Susan to solve the mystery of the disappeared Hogfather, and meanwhile to fill in for him. On the way to the pair's victory, readers encounter children both naughty and nice; gourmet banquets made of old boots and mud; lesser and greater criminals; an overworked and undertrained tooth fairy named Violet; and Bilious, the god of hangovers, among other imaginative concepts. The tone of much of the book is darker than usual for Pratchett--for whom ""humorous"" has never been synonymous with ""silly""--and his satire, too, is more edged than usual. (One scene deftly skewers the Christmas carol ""Good King Wenceslas."") Pratchett has now moved beyond the limits of humorous fantasy, and should be recognized as one of the more significant contemporary English-language satirists. U.K. rights: Victor Gollanz, The Cassell Group; trans., first serial, dramatic, audio rights: Ralph Vicinanza. (Nov.)